TOKSION AND MAGNETIZATION. 



279 



find magnetizatioD, we may conveniently place tlieni under the 

 following parallel statements : 



Strains produced by magnetization. 



(a) — (Experiment and theory). A 

 longitudinallv magnetized wire is 

 twisted hy circular magnetization. 



(h) — (Experiment and theory). A 

 circularly magnetized wire is twisted 

 by longitudinal magnetization. 



(o) — (Experiment and theory). Up 

 to moderate fields, the twist produced 

 hy the longitudinal and circular mag- 

 netizations of an iron wire is op- 

 posite to that in nickel. 



(d) — (Experiment and theory). 

 The twist due to longitudinal mag- 

 netization of a circularly magnetized 

 iron or nickel wire reaches a maxi- 

 mum in low fields. 



(e) — (Experiment and theory). In 

 strong fields, the twist due to longi- 

 tudinal magnetization of a circularly 

 magnetized iron wire is reversed and 

 takes place in the same direction as 

 in nickel. 



Effects of Stress on magnetization. 



(a/) — (Experiment and theory) 

 Twisting a longitudinally magnetized 

 wire gives rise to circular magneti- 

 zation. 



(?>'; — (Experiment and theory). 

 Twisting a circularly magnetized wire 

 gives rise to longitudinal magnetiza- 

 tion. 



(c') — (Experiment and theory). Up 

 to moderate fields, the transient cur- 

 rent, or the longitudinal magnetization 

 produced by twisting a longitudinally 

 or circularly magnetized wire respec- 

 tively, is opposite to that in nickel. 



(d/) — (Experiment and theory). 

 The transient current produced by 

 twisting a longitudinally magnetized 

 iron or nickel wire reaches a maxi- 

 mum in low fields. 



(e') — (Experiment and theory). In 

 strong fields, the direction of the 

 transient current produced by twisting 

 a longitudinally magnetized iron wire 

 is reversed and is in the same 

 direction as in nickel. 



In his paper on the principle of least action, Helmholtz^' 

 has placed the reciprocal relations of a dynamical system under 

 three heads. Denoting the generalized co-ordinates, the veloci- 



1) Helmholtz, Crelle's. Journal 100, p. 137, 1886 ; Abk., 3, p. 203, 1895. 



